You are answering a USMLE-style medical question. Question: A 2050-g (4.5-lb) female newborn and a 2850-g (6.3-lb) female newborn are delivered at 37 weeks' gestation to a 23-year-old, gravida 2, para 1 woman. The mother had no prenatal care. Examination of the smaller newborn shows a flattened nose and left-sided clubfoot. The hematocrit is 42% for the smaller newborn and 71% for the larger newborn. This pregnancy was most likely which of the following? Options: A) Monochorionic-diamniotic monozygotic B) Dichorionic-diamniotic dizygotic C) Monochorionic-monoamniotic monozygotic D) Conjoined twins Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.